Black spot on hemroid

I have what I'm pretty sure is an external hemroid. It seems pretty big, but I don't know how big they usually are. I'm pretty sure it was caused by constipation and straining. What I'm worried about is a black spot on the hemroid. The spot is probably 3 or 4 mm in diameter, and it really scares me, since black is not a color normally associated with my body...

I haven't seen a doctor yet, I haven't had time. Is this a normal thing? Has anyone else experienced it before? Please let me know, I'm really scared.